Compositions of doped, co-doped and tri-doped semiconductor materials

ABSTRACT

Semiconductor materials suitable for being used in radiation detectors are disclosed. A particular example of the semiconductor materials includes tellurium, cadmium, and zinc. Tellurium is in molar excess of cadmium and zinc. The example also includes aluminum having a concentration of about 10 to about 20,000 atomic parts per billion and erbium having a concentration of at least 10,000 atomic parts per billion.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional application of U.S. application Ser.No. 11/910,504, which is a U.S. National Phase of PCT/US2007/063330,which claims priority to U.S. Provisional Application No. 60/779,089,filed on Mar. 3, 2006, the disclosures of all of the foregoingapplications are incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH

This work was partially funded by the Department of Energy(DE-FG07-06IDI4724), and the United States government has, therefore,certain rights to the present invention.

TECHNICAL FIELD

The present disclosure is related to semiconductor materials forradiation detectors.

BACKGROUND

The selection of materials for radiation detector applications isgoverned by fundamental physical properties of the materials. It isdesirable that the material should exhibit high electrical resistivityand an excellent ability to transport charge carriers generated byexternal radiation. Materials that allow an applied electric field toextend through the whole volume of the crystal (i.e., full depletion)are also preferred. None of these properties can be found in high-purityand intrinsic (i.e., undoped) cadmium-zinc-tellurium (Cd_(1-x)Zn_(x)Te(0≦x≦1)) grown by known methods.

High-purity intrinsic CdZnTe compounds typically show low electricalresistivity due to intrinsic or native defects. It is believed that suchdefects can include cadmium (Cd) vacancies in tellurium (Te) rich growthconditions or cadmium interstitials in cadmium rich growth conditions.In addition, an intrinsic defect of Te antisite complexes forming, oftenin large concentrations, a deep electronic level at the middle of theband gap. This intrinsic defect can prevent full depletion of the devicewhen the defect is present in significant concentrations.

Unknown impurities and/or other native defects can also render theintrinsic CdZnTe compounds to have strong carrier trapping tendencies,thereby deteriorating a radiation detector's performance Whenimpurities, native defects, and their associations are incorporated inan uncontrolled manner, the properties of the CdZnTe compounds can varyfrom growth to growth and exhibit strong spatial variations within theingots. Accordingly, there is a need for a compensation scheme that haveresult in CdZnTe compounds with improved carrier transport propertiesand depletion characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electric field versus peak centroid diagram of asemiconductor material prepared in accordance with an embodiment of thedisclosure.

FIG. 2 is a set of Gamma spectroscopy measurement diagram ofsemiconductor materials prepared in accordance with an embodiment of thedisclosure.

FIG. 3 is a set of electron mobility diagram of semiconductor materialsprepared in accordance with an embodiment of the disclosure.

FIG. 4 is a set of spatial resistivity diagram of a semiconductormaterial prepared in accordance with an embodiment of the disclosure.

FIG. 5 is a set of Gamma spectroscopy measurements of semiconductormaterials prepared in accordance with another embodiment of thedisclosure.

FIG. 6 is an electron mobility diagram of a semiconductor materialprepared in accordance with another embodiment of the disclosure.

DETAILED DESCRIPTION A. Semiconductor Material

The present disclosure describes materials, compositions, and methodsfor preparing a bulk II-VI type semiconductor material containing CdTe,CdZnTe, CdZnSe or CdZnTeSe crystals (collectively referred to herein asCZT). The CZT material may be used in manufacturing solid state,elementary or matrix detectors for detection of gamma or X-rayradiations. It will be appreciated that several of the details set forthbelow are provided to describe the following embodiments in a mannersufficient to enable a person skilled in the relevant art to make anduse the disclosed embodiments. Several of the details and advantagesdescribed below, however, may not be necessary to practice certainembodiments of the invention. Additionally, the invention can includeother embodiments that are within the scope of the claims but are notdescribed in detail with respect to FIGS. 1-6 and attached AppendicesA-B.

In one embodiment, the CZT material includes a bulk II-VI typesemiconductor material, a first dopant selected from Group III and/orGroup VII of the periodic table, and a rare earth metal. The bulk II-VItype semiconductor material can include elements of Group II (e.g., Cd,Zn) and Group VI (e.g., Te, Se) of the periodic table. For example, thebulk II-VI type semiconductor material can include Cd and Zn, with Znhaving a concentration of between about 0 and about 20%. When Zn has aconcentration of 20%, 1 out of every 5 Cd sites is occupied by a Znatom. The bulk II-VI type semiconductor material can also include Te andSe, with Se having a concentration of between about 0 and 2%. When Sehas a concentration of 2%, 1 out of every 50 Te sites is occupied by aSe atom. The bulk II-VI type semiconductor material can have a Group VIelement to Group II element ratio between about 0.9 and about 1.1.

The first dopant can include a Group III element including boron (B),aluminum (Al), gallium (Ga), indium (In), and thallium (TI). The GroupIII element can have a concentration of about 10 to 10,000 parts perbillion (ppb). The first dopant can also include a Group VII elementincluding fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). TheGroup VII element can have a concentration of at least 10 ppb (e.g.,about 10 to about 10,000 ppb).

The second dopant can include a rare earth metal including cerium (Ce),praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm),europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium(Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Therare earth element can have a concentration of at least 10 ppb (e.g.,about 10 to about 400,000 ppb). In a particular embodiment, the seconddopant includes Er having a concentration of about 15,000 ppb to about400,000 ppb. In another particular embodiment, the second dopantincludes Er having a concentration of about 15,000 ppb to about 300,000ppb. In a further particular embodiment, the CZT material includescadmium, zinc, and tellurium with aluminum as the first dopant anderbium as the second dopant. The aluminum has a concentration of about10 to about 10,000 ppb, and the erbium has a concentration of about 10to about 400,000 ppb.

B. Compensation Scheme

The present disclosure also describes co-doping (use of two dopingelements) or triple doping (use of three doping elements in parallel)compensation schemes for at least partially remedy the intrinsic defectsof a high-purity CZT material. The first and second dopants can beselected and introduced to the bulk II-VI type semiconductor material ina controlled way and in quantities appropriate to a particular growthmethod to reliably produce useful extrinsic (i.e., doped) CZT materialswith improved resistivity (semi-insulating) and depletioncharacteristics.

Embodiments of the compensation schemes can enable the use of individualdopants to achieve full compensation and excellent charge transport inthe CZT materials. The first dopant can be an impurity selected fromelements in Group III and/or Group VII of the periodic table. Theselected first dopant can provide donors and makes A-centers. The seconddopant (e.g., a rare earth element) can passivate the intrinsic deeplevel defects to enable full depletion of the devices. Optionally, athird element can be used as a deep level dopant that secures fullelectrical compensation to control the resistivity.

Embodiments of this arrangement at least reduces the adverse effects ofthe common single doping schemes on the carrier transport properties ofthe CZT materials through the use of large concentrations ofcompensating doping elements. It is believed that the high concentrationof dopants in the single-dopant schemes mask the effects of theintrinsic deep level defects without passivating them, thereby causingincomplete depletion of the detectors and space charge build up duringoperation of the device and the collapse of the internal electric fieldin the radiation detector, commonly called as polarization.

In one embodiment, a particular compensation scheme can includeselecting a first dopant having an element from Group III and/or GroupVI of the periodic table to improve resistivity of the CZT materials.Without being bound by theory, it is believed that undoped CZT materialscan vary in resistivity due to native defects, such as cadmiumvacancies, dislocations, and intrinsic deep level defects incorporatedto the material during crystal growth. Some of these crystal defects canbe ionized at ambient temperature to provide a supply of free chargecarriers (electrons or holes) resulting in low-resistivity. It isbelieved that a Group III and/or Group VII element can occupy the sitesnormally occupied by elements from Group II or Group VI in the CZTmaterial, and so vacancies, antisites, and/or other defects can bereduced. For example, Group III elements (e.g., Al, In) and/or Group VIIelements (e.g., Cl, Br) can combine with the cadmium vacancies to formimpurity-vacancy pairs commonly known and referred to as A-centers. Inthis process, the energy level of the cadmium vacancy defect can beshifted to the lower energy level of the A center. The lower energylevel reduces the residency time of charge carriers (holes) at thedefect and improves the carrier transport property of the CZT material.

However, the CZT materials doped with an element of Group III and/orGroup VII typically cannot achieve full depletion in operation becauseother Group II related intrinsic defects can result in charge trapping.For example, formation of deep level defects from intrinsic or nativedefects in sufficient concentrations can produce crystals that cannot befully depleted by an external bias voltage. As a result, the chargetransport properties of the CZT material is reduced. Thus, selecting asecond dopant to provide new carrier pathways through the CZT materialand/or through structural perturbation of the Group II related defectscan reduce such charge trapping.

The second dopant can be selected to include a rare earth metal elementbased on whether the formation energy (e.g., enthalpy and/or entropy offormation) of a Group II and/or Group VI element and the rare earthmetal is above a threshold. In a particular example, Er is selected asthe second dopant because Er can react with Te to form Er—Te complexes.The reaction can have a large heat of formation, and Er can irreversiblycombine with Te while in a liquid phase, the product of which may formsolid domains that can remain intact during subsequent cooling to beintegrated into the bulk CZT material. It is believed that thisinteraction can decrease the frequency of intrinsic defects related tothe Group VI element in the CZT material.

The second dopant (e.g., Er) can have a concentration of at least 10atomic parts per billion. In some embodiments, the Er concentration canbe about 10,000 to about 400,000 atomic parts per billion. In furtherembodiments, the Er can have a molar concentration that is generallysimilar to that of tellurium in the CZT material. Surprisingly, suchhigh doping levels can limit the spatial variations within grown ingots.

Typically, conventional techniques do not use such a high dopingconcentration because a number of factors pose practical limitations onthe useful range of dopant concentrations. Major factors include bothsolubility and utility provided by any given dopant element. It isbelieved that there are limits to the solubility of an element within aliquefied mixture of Group II and Group VI elements. The limitedsolubility in turn restricts the potential dopant range. Additionally,the maximum and minimum dopant levels that can provide useful materialscan vary with the specific electronic properties of the dopant. Inparticular, for dopants that impart positive or beneficial properties tothe material (e.g., to increase resistivity or charge carrier transportability), there is typically a doping level over which the dopant beginsto impart adverse effects on the utility of the material. Generally,once a doping level exceeds this critical value, the dopant will act ascharge trap and diminish the charge carrier transport ability of thematerial. With these restrictions, doping practice common to the arttypically utilizes doping levels of between 10-10,000 ppb to avoiddegradation of the desired material properties.

One expected advantage of several embodiments of the compensation schemeis the improved accuracy in predicting whether incorporating aparticular second dopant would yield a useful material. Conventionaltechniques for selecting the second dopant generally involve acomparison of the electronic properties between the selected seconddopant and the Group II and/or Group VI elements in the CZT material.Typically, the second dopant is selected to pin the Fermi level at amidpoint between the energy levels of the valance band and theconduction band. However, such a technique does not provide adequateinformation relating to the resulting solid state electronic propertiesand the interaction between the second dopant and the Group II and GroupVI elements. As a result, in many cases, there is little informationavailable for accurate prediction of whether incorporating the seconddopant would yield a useful material. Thus, the selection criterionbased on formation energy discussed above can at least provide a generalguide for choosing a second dopant that might yield useful materials.

Materials with full depletion have optimal charge transport properties.Specifically, fully depleted materials can transport both “holes”(positive charges) and “electrons” (negative charges). This propertyenables a more rapid equilibration of charges after the perturbation ofcharge associated with the detection of a photon. The net result is amaterial with a rapid refresh rate, which allows for said material to beapplied as a detector in applications requiring a rapid, repetitivedetection (e.g. medical imaging and time resolved imaging).

Compensating for Group VI element related defects and larger volumedefects such as precipitates and inclusions utilizing the compensationschemes can limit the spatial variations within grown ingots. With fewerdefects, a larger active area can be realized to enable applicationsthat require larger detectors. Moreover, dopant combinations thatminimize group II related defects and provide full depletion haveparticular utility in devices that have a large detector size and a highdetection rate requirement. Specific examples include gamma and/or X-rayimaging methods (e.g., Computed Tomography).

During preparation of a charge, in accordance with some embodiments, afew degrees of freedom are allowed in the progression of runs andinclude the quantity and type of the dopant. Small concentrations ofchosen binary (or tertiary) dopants are added to the growth. To ensurethe dopants are uniformly spread throughout the ingot, the meltedcharge, in one embodiment, goes through a quick freeze and a re-meltstep before the actual growth starts to stop element segregation and toincrease solubility. The results of the prepared charges are reflectedin the examples below.

EXAMPLES Example 1 Crystal Growth of Doped Materials

The charge, which contains Cd and/or Zn, Te and/or Se, and one or moredopants from group III and/or VI and/or a rare earth element, was loadedinto a crucible in an argon filled glove bag. The crucible and chargewere then placed in an ampoule and sealed under vacuum at less than 10-7Torr with a quartz end cap. Ingots were grown under vacuum or with apartial pressure of an inert gas. The preparation of the charge was donein a glove bag or clean room conditions to reduce residual impurities.For low pressure growth methods, the crucible was then placed into aquartz ampoule and connected to a vacuum system. The air was evacuatedfrom the ampoule and a partial pressure of an inert gas or a mixture ofgases was supplied to the ampoule and then sealed shut by a torch. Forhigh pressure growth techniques, up to 100 atmospheres was used todecrease charge loss, and the ampoule may be optional. In otherembodiments, this procedure may be varied.

The setup of the ampoule can limit vapor transport that occurs duringthe growth. The over pressure of molten CZT allows for vapor transportto condense at the coldest region within the ampoule, resulting inmaterial lost from the ingot. The majority of the charge loss wasdeposited at the tip and shoulder regions of the ampoule outside of thecrucible. Four crystal growth runs were done using different positionsof the end cap to affect the open volume. The crystal growth setup waslisted in Table 1. In the 1^(st) growth run, the end cap was positionedapproximately 4 inches from the end of the crucible. In the 2^(nd) run,a lid constructed from the same material as the crucible was placed onthe crucible and the end cap was positioned at the same approximatedistance of 4 inches away from the crucible. During the 3^(rd) run, alid was placed and the end cap was positioned much closer, approximately1 inch from the end of the crucible. In the 4^(th) run the ampoule wasbackfilled with a partial pressure of an inert gas, and a lid for thecrucible and the end cap were positioned approximately 1 inch from thelid.

Example 2 Materials Characterization

The 1^(st) run had a charge loss of 11.0%; the addition of the lid inthe 2^(nd) run slightly decreased the charge loss to 9.0%. The 3^(rd)run greatly improved reduction of the loss to 4.2%. In the 4^(th) runthe ampoule had been backfilled with a partial pressure. This backfilling step was done with the lid and end cap positioned approximately1 inch from the crucible. This process further decreased the charge lossto 0.5%, as shown in Table 1.

TABLE 1 Crystal growth setup All growths have the same ratio Te/(Cd +Zn) = 1.033 Run 1^(st) 2^(nd) 3^(rd) 4^(th) Crucible GLC GLC GLC PYCAmpoule pressure 10⁻⁷ Torr 10⁻⁷ Torr 10⁻⁷ Torr <200 Torr Ar End capposition 4 inches 4 inches 1 inch 1 inch Lid No Yes Yes Yes Charge loss11.0% 9.0% 4.2% 1.5%

Each ingot was cut vertically through the center for characterizationand sample preparation. Samples from each ingot were cut using a diamondwire saw. Then each sample was prepared by polishing with alumina powderand/or etching in a bromine methanol solution to remove saw damage.Finally they were sputtered with gold planar contacts. Many variationson the specific dimensions of the material cross section, thearrangement and composition of the contacts can be implemented here. Oneskilled in the art can tailor these particular aspects of the solidstate detection element for use in a specific manifestation of radiationdetection instruments. Table 2 gives the average values from samplesmade from each ingot. The conductivity type of each ingot has beenconfirmed by thermoelectric effect spectroscopy (TEES). The BulkResistivity of each sample was determined by applying voltages from −1to 1 volts. The μτ products for electrons were determined by 0.5 μecshaping with a ²⁴¹Am source.

TABLE 2 Properties of 5 ingots ⁵⁷Co Conduc- Bulk 122 keV μτ for Growthtivity Resistivity Ave. resolution electrons Ave. GLC 1 p-type 1.7 ×10¹⁰ Ohm*cm No No response response GLC 3 n-type 1.0 × 10¹⁰ Ohm*cm 15.8keV 6.80 × 10⁻⁵ cm²/V 12.9% PBN p-type 2.2 × 10⁷ Ohm*cm No No responseresponse PYC 1 n-type 1.0 × 10¹⁰ Ohm*cm 19.5 keV 2.59 × 10⁻⁴ cm²/V 16.0%PYC 4 n-type 2.0 × 10¹⁰ Ohm*cm 11.6 keV 2.68 × 10⁻⁴ cm²/V  9.5%

Samples were also placed in a Multi Channel Analyzer (MCA) to checkresponse to incident radiation. No pulse processing or post processingwas used to enhance the energy resolution. The pulser resolutionaveraged 2.4% for the ⁵⁷Co spectra and was 1.2% for the ¹³⁷Cs spectra.The first ingot to have a significant response to ionizing radiation wasGLC 3. The two ingots grown in PBN were high purity, but lowresistivity, p-type, that shows no response to ionizing radiation.According to the GDMS analysis the group III dopant does not seem assoluble in CZT when using the PBN crucible. All PBN growths had lowerthan intended doping levels. All samples that show any significantresponse to incident radiation have been from n-type growths with groupIII doping.

The ⁵⁷Co isotope was used to analyze the response of the detectors atroom temperature. The x-rays from this source display the mobility andlifetimes of both electron and hole carriers. GLC 3 has good energyresolution at the 122 keV peak, however, the 14 keV peak was notobserved, indicating that the sample was not completely active. The peakposition of the 122 keV energy was low in channel numbers, showing theλτ of both the holes and electrons were similar for this resolution atthis channel number. The λτ product for the electrons was not highenough to resolve the 14 keV peak, making the sample not fully activethrough the 1.9 mm detector thickness. The GLC 3 spectrum for the ¹³⁷Cssource, displays the 662 keV peak was not sharp in resolution, but highin counts because of the large hole λτ. PYC 1 and 4 122 keV peakposition were higher in channel number, but not equal λτs. The holetailing in both spectra indicates that the hole λτ was lower than theelectron's. PYC 4 has high resolution and the best λτ for electrons. λτproducts have been determined by the Hecht relation as follows:

$Q = {Q_{O}*\frac{\mu \; \tau*E}{Th}*\left( {1 - {\exp \left( \frac{- {Th}}{{\mu\tau}*E} \right)}} \right)}$

Q was the charge collection (peak centroid), Q_(O) was the maximumcollectible charge, λτ was the mobility*lifetime, E was the appliedelectric field; Th was the thickness of the sample.For electron characterization, a ²⁴¹Am source was positioned facing thecathode end of the detector. Plotting the peak centroid position of the59.5 keV line on the y-axis, and the applied electric field on the x,the Hecht relation was fitted to equation 1. The λτ product forelectrons can be determined and shown, in FIG. 1 for growth PYC 4. Ashaping constant of 0.5 μseconds was used for simplicity of keeping allmeasurements consistent. By simply increasing the shaping constant, λτcan be increased.

Physical Characterization of the Material, Where Er Was Co-Dopant

CZT undoped has a low resistivity caused primarily by defects includingthe cadmium vacancy. A group III dopant was intended to compensate thisdefect and likely would increase the resistivity of the material. Thiscompensation technique creates an A-center. However this compensationalone does not produce intrinsic characteristics or fully active regionsof the material. The introduction of a second dopant, Erbium, doescompensate remaining defects creating a fully active material. (FIGS.3-6 and Table 7) This combination of dopants results in highresistivity, and large charge carrier mobility and lifetimes. Theproperties of large electron and hole mobility and lifetimes throughoutthe bulk of the material create fully active material, suitable forsolid state radiation detectors. Elemental compositions as measured byglow discharge mass spectrometry are provided in Appendix B.

TABLE 3 7 crystal growths co-doping with erbium. μτ PRODUCT ResistivityEr (ppb) Al (ppb) Cl (ppb) (0.5 shaping) (Ω*cm) 460 2200 — 2.60E−042.38E+10 600 2400 — 1.80E−04 2.45E+10 260 4200 100 1.50E−04 1.78E+10 3302400 — 4.95E−05 1.22E+10 220,000 2500 — 2.91E−04 1.76E+10 392,000 2400 —1.34E−04 1.19E+10 μτ was the product of μ = mobility and τ = lifetime.The product of these two properties was a common method to quantify thematerial. The larger the μτ number the better the charge carriermobilityand lifetimes are. Fully active material has large μτ values(~1.0 × 10⁻³ cm²/V).

Tellurium inclusions and precipitates can be the most common anddetrimental bulk defects in CdTe and CdZnTe materials. These kinds ofinclusions can create charge trapping and degradation in detectorperformance. It was believed that higher temperature gradients acrossthe melt during growth can limit the tellurium precipitates that usuallyoccur along grains boundaries. Tellurium inclusions are opaque underinfrared, whereas the bulk material is transparent. Thus infraredmicroscopy was used on the samples and wafers cut from ingots to map andmonitor these inclusions in the material.

Gamma spectroscopy was performed on all samples cut from grown ingots.Numerous samples have a resolution and efficiency similar to thecommercially available CdZnTe detectors. Four examples are shown in FIG.2.

Electron mobility multiplied by the lifetime of the charge carrier wascalculated from grown samples. The product was calculated by fittingapplied bias voltage versus the 59.5 keV x-ray peak from the ²⁴¹Amsource. FIG. 3 shows results from two ingots.

Trapping levels associated with Cadmium vacancies, tellurium anti-sitesand their complexes were identified using thermo-electrical effectspectroscopy in CdTe and CdZnTe crystals grown by the vertical and highpressure Bridgman techniques. The corresponding thermal ionizationenergies, which were extracted using initial rise and/or variableheating rate methods and first principles calculations are atE1=0.09±0.01, E2=0.12 ±0.01 eV, E3=0.18±0.01 eV, E4=0.23±0.01 eV,E5=0.36±0.01 eV, E6=0.79±0.08 eV, E7=0.39±0.01 eV, and E8=0.31±0.01 eV.Based on the first principles method calculation of transition energies(thermal ionization energies), purity data from glow discharge massspectroscopy, and growth conditions of the crystals trapping levels havebeen determined.

Trapping levels were identified at E2 and E4 with the first and secondionized state of the isolated cadmium vacancy, E1 and E3 to the firstand second ionized state to cadmium vacancy-isoelectronic oxygencomplex. Other levels assigned were E5 with telluriumantisite-divacancy, E6 with tellurium anti-site-single vacancy complex,E7 with tellurium antisite-cadmium vacancy-donor in the cadmium sitecomplex and E8 with tellurium antisite-cadmium vacancy. The lattercomplex acts as a donor.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thescope of the invention. Aspects of the invention described in thecontext of particular embodiments may be combined or eliminated in otherembodiments. While advantages associated with certain embodiments of theinvention have been described in the context of those embodiments, otherembodiments may also exhibit such advantages, and not all embodimentsneed necessarily exhibit such advantages to fall within the scope of theinvention. The following examples reflect further embodiments of theinvention.

APPENDIX A Summary of Crystal Growth (CG) Conditions and MaterialCompositions Associated With Selected CG's GROWTH CG1 CG2 CG3 CG4 ChargeHoneywell Honeywell Honeywell Honeywell Excess Te Te/ 1.0018 1.018 1.0181.018 (Cd + Zn) Dopants ppb Crucible Glassy Carbon #1 GlyC #2 GlyC #3GlyC #4 Lid none none none none Partial Pressure vacuum vacuum vacuumvacuum N or P Type Ave. Resistivity 57Co response Ave. μτ electronsIMPURITIES ppb Li B C N O Na Mg Al Si P S Cl K Ca Ti V Cr Fe Ni Cu Ge AsSe Nb Sn Er Pt Pb Total Total w/o Dopants Average: Zn % GROWTH CG1 CG2CG3 CG4 GROWTH CG5 CG6 CG7 CG8 Charge 1191 grams 1199 grams 1199 grams1071 grams Excess Te Te/ 1.018 1.033 1.033 1.033 (Cd + Zn) Dopants ppbAl, Pb, V 1500, 1000, 500 Al, Pb, V 1500, 1000, 500 Al, Pb, V 1500,1000, 500 Al, Pb, V 1500, 1000, 500 Crucible GlyC #5 GlyC #6 GlyC #7GlyC #7 Lid none none None yes Partial Pressure vacuum vacuum vacuumvacuum ×10 − 7 torr N or P Type P-type P-type P-type Ave. Resistivity1.7E10 Ohm*cm 1.2E9 Ohm*cm 1.8E9 Ohm*cm 57Co response N/A poor N/A N/AAve. μτ electrons N/A N/A N/A N/A IMPURITIES ppb Tip Mid Heel Tip MidHeel Tip Mid Heel Tip Mid Heel Li 5 7 25 6 5 9 5 0 12 0 10 24 B 1 24 634 C 100 7500 380 100 210 42 300 230 22 1600 65 1200 N 15 50 25 30 29 1610 15 5 35 4 40 O 370 690 130 120 1000 44 83 140 30 1300 55 140 Na 5513000 65 20 550 67 17 16 20 110 11 82 Mg 990 660 120 40 78 70 36 44 300660 54 150 Al 140 11000 13000 2000 57000 5400 120 160 1500 20000 14004000 Si 800 1100 29 93 740 39 170 129 0.7 1700 49 1300 P 2 11 2 4 7 2 147 10 S 97 450 660 350 540 300 130 0 510 520 400 450 Cl 40 2 75 90 100 5228 77 70 250 120 86 K 8 180 10 63 Ca 12 3400 33 74 170 120 220 0 200 Ti5 380 4 24 14 8 1 0.6 0.3 270 28 28 V 140 130 2400 3700 8300 1800 120120 85 1800 180 26 Cr 18 5 18 6 16 10 20 8 24 29 30 78 Fe 10 10 10 82 50140 50 62 210 150 78 240 Ni 320 380 640 0 0 4 Cu 1 0.5 1 21 15 Ge 12 6418 As 8 32 72 Se 1 38 11 Nb 0.3 10 1 Sn 20 15 15 Er Pt 4 5 7 160 0 2100Pb 340 1500 170 300 420 180 40 34 23 1000 160 1700 Total 3514 4064417927 7039 69347 8314 1130 1036 2816 29818 2651 11854 Total w/o Dopants2894 28014 2357 1039 3627 934 850 722 1208 7018 911 6128 Average:11088.26667 1866.666667 926.5333333 4685.666667 Zn % 1.9 3.1 6.2 2.3 3.72.5 2.1 3.9 6.7 6.1 3.0 2.6 GROWTH CG5 CG6 CG7 CG8 GROWTH CG10 CG11 CG12CG13 Charge 1070 grams 1071 grams 665 grams Excess Te Te/ 1.033 1.0331.033 (Cd + Zn) Dopants ppb Al, Pb, Sn 500, 300, 100 Al, Pb, Ge 500,400, 200 Al, Pb, Ge 500, 400, 300 Al, Pb, Fe 1000, 500, 500 CrucibleGlyC #7 GlyC #8 GlyC #9 PBN #1 Lid yes yes yes yes + snap ring PartialPressure vacuum 7.8 × 10 − 7 torr vacuum 3.8 × 10 − 8 torr vacuum 9.3 ×10 − 8 torr vacuum 3.8 × 10 − 8 torr N or P Type N-type + P-type N-typeP-type Ave. Resistivity 1.0E10 Ohm*cm 1.0E10 Ohm*cm 3.9E5 Ohm*cm 57Coresponse two peaks two peaks N/A Ave. μτ electrons 6.8E−5 cm2/V 4.7E−-5cm2/V N/A IMPURITIES ppb Tip Mid Heel Tip Mid Heel Tip Mid Heel Li 5 5 3B 0 0 100 C 140 110 30 890 120 680 490 720 580 N 31 35 60 14 15 10 310130 140 O 110 100 80 440 80 330 420 380 410 Na 5 0 3 4 13 8 0 15 15 Mg110 69 60 59 50 50 55 42 84 Al 1200 1500 1600 290 680 1500 150 48 53 Si6 24 3 8 0 0 170 34 210 P S 230 260 300 190 240 420 200 270 460 Cl 22 3537 13 9 27 19 27 50 K Ca Ti 11 2 34 V 2 0.4 0.3 5 5 4 Cr 14 0 4 30 13 15Fe 52 53 120 63 83 450 150 220 490 Ni Cu Ge <50 <35 <40 As Se Nb Sn <20<15 <18 Er Pt Pb 6 8 4 3 5 0 14 7 88 Total 1933 2199 2404 2009 1313 34941989 1895 2614 Total w/o Dopants 727 691 800 1716 628 1994 1675 16201983 Average: 739.5666667 1446 1759.333333 Zn % 5.0 4.4 3.7 3.4 3.4 3.24.7 3.8 3.5 GROWTH CG10 CG11 CG12 CG13 GROWTH CG14 CG15 CG16 CG16aCharge 665 grams 887 grams 887 grams 887 grams Excess Te Te/ 1.033 1.0331.033 (Cd + Zn) Dopants ppb Al, Pb, Fe 2000, 500, 500 Al, Pb, Fe 1500,300, 500 Al, Pb, Ge 1000, 1000, 500 Al, Pb, Ge 1000, 1000, 500 CruciblePBN #1 PyC #1 PyC #1 PyC #1 Lid yes #2 + 2 snap rings yes yes yesPartial Pressure vacuum 5.0 × 10 − 8 torr 90 mtorr Ar 90 mtorr Ar vacuum1.4 × 10 − 7 torr N or P Type P-type N-type P-type Ave. Resistivity2.2E7 Ohm*cm 1.03E10 Ohm*cm 1.0E8 Ohm*cm 57Co response poor three peaksN/A Ave. μτ electrons N/A 2.6E−4 cm2/V N/A IMPURITIES ppb Tip Mid HeelTip Mid Heel Tip Mid Heel Li B 66 29 0 5 0 0 C 300 720 200 570 95 300 201000 360 N 36 34 15 60 15 20 5 47 29 O 530 500 110 370 60 170 32 1100300 Na 8 43 24 11 8 13 5 15 21 Mg 130 40 89 45 40 46 90 80 81 Al 210 170630 4400 3100 2100 23 13 0 Si 61 8 62 150 9 8 15 13 3 P 0 3 3 13 8 0 918 7 S 98 390 420 300 240 200 220 420 320 Cl 460 240 73 34 380 110 K CaTi 27 0.8 77 1 0 0 V 0.7 0.6 0 Cr 0 5 4 0 10 0 0 9 5 Fe 390 400 630 1900820 720 100 240 120 Ni Cu Ge <25 35 <25 As Se Nb 21 0.5 110 Sn Er Pt Pb64 11 170 0 24 7 24 48 20 Total 1941 2354 2544 8286 4670 3657 577 34181376 Total w/o Dopants 1277 1773 1114 1986 726 830 530 3322 1356Average: 1388.1 1180.433333 1736 Zn % 6.0 3.5 3.4 2.8 2.6 3.1 3.0 3.23.1 GROWTH CG14 CG15 CG16 CG16a GROWTH CG18 CG19 CG20 CG21 Charge 887grams 887 grams 887 grams 887 grams Excess Te Te 1.033 1.033 1.033 1.033(Cd + Zn) Dopants ppb Al, 0.1% Pb, Fe Al, Pb Al, Fe Al, Pb, Ge 1000,0.1%, 300 1000, 3000 1000, 300 1000, 15000, 300 Crucible PyC #2 PyC #1PyC #1 PyC #2 Lid yes yes yes yes Partial Pressure 0.05 atm Ar/1% Hy 0.1atm Ar/1% Hy 0.19 atm Ar/1% Hy 0.16 atm Ar/1% Hy N or P Type N-typeN-type N-type P-type Ave. Resistivity 1.5E9 Ohm*cm 1.63E10 Ohm*cm 2E10Ohm*cm 1E9 Ohm*cm 57Co response N/A one peak discriminator grade N/AAve. μτ electrons N/A 2.8E−4 cm2/V 2.7E−4 cm2/V N/A IMPURITIES ppb TipMid Heel Tip Mid Heel Tip Mid Heel Tip Mid Heel Li 17 0 6 B 0 300 0 65100 0 C 17 43 100 130 21 49 738 220 160 460 170 150 N 4 7 12 9 10 5 4935 10 4 5 5 O 50 120 110 120 160 79 550 200 140 380 170 100 Na 12 11 1115 14 17 20 16 9 6 5 7 Mg 54 52 40 16 15 62 0 16 29 28 16 15 Al 880 14002300 110 1200 1800 0 1500 7600 560 590 1200 Si 57 37 0 28 11 50 8 0 1520 5 3 P 4 0 0 0 9 0 S 75 150 70 0 35 70 Cl 3 12 0 28 120 110 17 75 29 KCa 0 0 40 Ti V Cr 3 4 5 Fe 580 630 720 0 52 66 <5 250 560 49 38 62 Ni 06 0 Cu Ge 67 65 44 As Se 61 0 0 Nb Sn Er Pt Pb 120 m 73 m 220 m 58 75150 980 790 510 Total 596 2138 2463 1525 2456 8628 2554 1854 2096 Totalw/o Dopants 197 282 313 428 863 513 1525 956 1028 947 409 342 Average:264 601.3333333 1169.666667 566 Zn % 6.0 5.0 6.0 4.7 5.8 3.0 0.8 3.2 2.45.1 3.9 4.8 GROWTH CG18 CG19 CG20 CG21 GROWTH CG22 CG23 CG24 CG25 Charge882 grams 882 grams 883 grams 883 grams Excess Te Te/ 1.023 1.023 1.0251.025 (Cd + Zn) Dopants ppb Al, Pb 1000, 3000 Al, Fe 1000, 300 Al, Er2000, 15000 Al, Pb 1500, 15000 Crucible PyC #2 PyC #1 PyC #1 PyC #2 Lidyes yes yes yes Partial Pressure 0.256 atm Ar/1% Hy 0.263 atm Ar/1% Hy0.105 atm Ar/1% Hy 0.1 atm Ar/1% Hy N or P Type P-type N-type N-typeAve. Resistivity 5E7 Ohm*cm 1.5E10 Ohm*cm 1.8E10 Ohm*cm 1.6E10 Ohm*cm57Co response N/A three peaks discriminator grade two peaks Ave. μτelectrons N/A 1.7E−4 cm2/V 2.8E−4 cm2/V IMPURITIES ppb Tip Mid Heel TipMid Heel Tip Mid Heel Tip Mid Heel Li 0 4 4 4 0 11 0 0 9 B 120 0 0 0 0130 C 210 58 90 25 30 7 79 26 15 77 18 19 N 24 11 8 35 20 4 20 20 10 5018 15 O 160 36 52 45 65 45 95 55 30 180 110 55 Na 18 19 13 12 6 13 9 1218 3 0 17 Mg 15 18 23 13 21 22 14 21 26 32 24 33 Al 2300 5000 4300 490360 740 2100 5400 18000 830 2300 8100 Si 27 0 5 20 21 19 160 13 10 10 46 P 22 12 5 6 0 0 2 0 0 S 130 80 41 70 40 0 68 110 150 44 44 57 Cl 13050 56 26 23 35 23 43 44 24 20 35 K Ca Ti 6 0 0 V Cr 0 6 0 6 0 0 14 6 7Fe 360 970 940 51 37 130 63 83 240 Ni Cu 0 0 90 Ge As 0 8 0 Se Nb Sn Er5400 7600 9800 Pt Pb 80 85 72 390 400 940 Total 3122 5379 4669 1226 15641836 8025 13337 28453 1719 3027 9533 Total w/o Dopants 822 379 369 376234 156 525 337 653 499 327 493 Average: 523.3333333 255.3333333 505439.6666667 Zn % 3.0 2.9 3.1 3.5 6.2 4.0 3.3 3.0 2.4 4.6 4.2 3.3 GROWTHCG22 CG23 CG24 CG25 GROWTH CG26 CG27 CG28 CG29 Charge 883 grams 883.5grams 770 grams 880.47 grams Excess Te Te/ 1.025 1.025 1.018 1.018 (Cd +Zn) Dopants ppb Al, Er 1500, 1500 Al, Er 1500, 1500 Al, Er 1500, 1500Al, Er 1500, 1500 Crucible PyC #1 PyC #2 PBN #1 PyC #2 Lid yes yes yes#3 slit, 2 snap rinqs yes Partial Pressure 0.105 atm Ar/1% Hy 0.1 atmAr/2% Hy 0.24 atm Ar/2% Hy 0.25 atm Ar/2% Hy N or P Type N-type Ave.Resistivity 1.6E10 Ohm*cm 1.0E10 Ohm*cm 2.0E6 Ohm*cm 3.0E10 Ohm*cm 57Coresponse discriminator grade discriminator grade N/A discriminator gradeAve. μτ electrons 1.94E−4 cm2/v 2.0E−4 cm2/V N/A 2.75E−4 cm2/VIMPURITIES ppb Tip Mid Heel Tip Mid Heel Tip Mid Heel Tip Mid Heel Li 50 5 8 4 B 980 9 C 250 260 750 230 290 240 130 110 160 86 26 100 N 49 3030 70 37 63 80 30 26 37 19 21 O 900 300 630 250 320 590 250 160 130 16050 200 Na 200 37 17 21 7 20 21 25 24 5 Mg 20 18 23 19 38 33 14 26 44 6134 31 Al 2200 2400 4200 1000 2600 3700 160 270 250 2300 12000 7500 Si 785 16 6 21 32 25 7 7 5 63 22 P 7 3 0 7 5 2 7 S 200 150 260 140 110 51 12022 240 49 100 140 Cl 60 30 100 53 71 50 61 20 94 7 12 79 K Ca 130 62 4572 Ti V Cr 9 4 10 3 14 5 4 Fe 120 61 150 250 87 160 260 96 96 240 Ni Cu47 56 Ge As Se 20 0 10 48 Nb Sn Er 460 600 260 420 630 680 5500 330 530720 1700 630 Pt Pb Total 4578 3898 6461 2216 4124 5887 7436 1168 18883582 14192 9019 Total w/o Dopants 1918 898 2001 796 894 1507 1776 5681108 562 492 889 Average: 1605.666667 1065.666667 1150.666667647.6666667 Zn % 6.0 3.2 4.7 3.8 7.2 5.5 3.0 4.6 2.9 3.8 2.8 3.6 GROWTHCG26 CG27 CG28 CG29 GROWTH CG30 a & b CG31 CG32 Charge 883.59 875.82875.82 Excess Te Te/ 1.025 1.009 1.009 (Cd + Zn) Dopants ppb Al, Er1500, 1500 Al, Er 2000, 4500 Al, Er 2000, 4500 Crucible PyC #3 & #5 PyC#4 PyC #3 Lid yes yes yes Partial Pressure 0.25 atm Ar/2% Hy 0.25 atmAr/2% Hy 0.13 atm Ar/2% Hy p. trans N or P Type Ave. Resistivity 2.0E10Ohm*cm 1.0E10 Ohm*cm 57Co response two peaks discriminator grade Ave. μτelectrons 3.5E4−cm2/V 1.0E−3 cm2/V IMPURITIES ppb Tip Mid Heel Tip MidHeel Li 7 62 B C 290 120 120 470 62 21 N 56 67 49 34 83 6 O 440 230 340390 75 33 Na 9 12 44 50 160 Mg 56 36 51 47 28 87 Al 250 690 3500 14004400 50000 Si 12 12 11 21 P 4 S 100 100 Cl 36 320 1400 340 1700 5000 KCa 100 Ti V Cr Fe 110 110 150 100 56 130 Ni Cu 86 Ge As Se Nb Sn Er 310450 440 1900 2400 3700 Pt Pb Total 1560 2044 6162 4725 8876 59506 Totalw/o Dopants 1000 904 2222 1425 2076 5806 Average: 1375.3333333102.333333 Zn % 7.8 5.4 6.0 4.9 3.7 2.8 GROWTH CG30 a & b CG31 CG32GROWTH CG32a CG33a CG33b Charge 874.99 872.9 + 0.21 Te Excess Te Te/1.009 1.0074 1.0074 (Cd + Zn) Dopants ppb Al, Er 2000, 4500 plus Al 2000Al, Er 2000, 10000 Al, Er 2000, 10000 Crucible PyC #5 PyC #2 PyC #6 Lidyes yes yes Partial Pressure 0.17 atm Ar/2% Hy 0.14 atm Ar/2% Hy p.trans 0.18 atm Ar/2% Hy N or P Type Ave. Resistivity 57Co response threepeaks Ave. μτ electrons 3.0E−3 cm2/V IMPURITIES ppb Tip Mid Heel Tip MidHeel Li 7 6 13 B 21 C 12 20 940 N 4 4 20 O 20 30 620 Na 10 6 5400 Mg 2950 990 Al 320 590 1200 Si 39 490 P 6 S 50 24 43 Cl 350 710 400 K Ca 340Ti 540 V Cr 11 Fe 50 110 330 Ni 19 Cu 40 Ge As Se Nb 730 Sn Er 4000 87002500 Pt Pb 4100 Total 4897 10250 18747 Total w/o Dopants 577 960 15047Average: 0 5528 Zn % 3.5 4.2 4.5 GROWTH CG32a CG33a CG33b

I/we claim:
 1. A method for processing a semiconductor material,comprising: placing at least one element from Group II of the periodictable and at least one element from Group VI of the periodic table in acontainer; mixing the at least one element from Group II and the atleast one element from Group VI of the periodic table with a firstdopant and a second dopant to form a mixture, wherein the first dopantincludes at least one element from Group III or VII of the periodictable, and wherein the second dopant includes erbium at a concentrationof about 10 to about 400,000 atomic parts per billion or dysprosium at aconcentration of about 10 to about 10,000 atomic parts per billion; andconverting the mixture into a solid material.
 2. The method of claim 1wherein the first dopant includes aluminum at a concentration of about10 to about 20,000 atomic parts per billion, and wherein the seconddopant includes erbium.
 3. The method of claim 1 wherein the firstdopant includes indium at a concentration of about 10 to about 20,000atomic parts per billion, and wherein the second dopant includes erbium.4. The method of claim 1 wherein the at least one element from Group IIof the periodic table includes cadmium, and wherein the at least oneelement from Group VI of the periodic table includes tellurium.
 5. Themethod of claim 4 wherein the mixture further includes zinc, and whereinthe mixture has a molar excess of tellurium over cadmium and zinc, themolar excess being between about 0.5% to about 75%.
 6. The method ofclaim 1 wherein the first dopant includes chlorine at a concentration ofabout 10 to about 20,000 atomic parts per billion, and wherein thesecond dopant includes erbium.
 7. A method for preparing a co-dopedsemiconductor material having at least one element from Group II of theperiodic table and at least one element from Group VI of the periodictable, wherein the method comprising: selecting a dopant from the groupconsisting of aluminum, chlorine, and indium; selecting a co-dopantbased on a formation energy of a complex between the at least oneelement from Group VI of the periodic table and the co-dopant; anddoping the semiconductor material with the selected dopant and theco-dopant.
 8. The method of claim 7 wherein selecting a co-dopantelement includes determining whether the co-dopant irreversibly combineswith the at least one element from Group VI of the periodic table in aliquid phase.
 9. The method of claim 7 wherein the at least one elementfrom Group VI includes Tellurium, and wherein the co-dopant includeserbium.
 10. The method of claim 7 wherein doping the semiconductormaterial includes doping the semiconductor material with the selectedco-dopant at a concentration of about 10 to about 400,000 atomic partsper billion.
 11. The method of claim 7, further comprising decreasingintrinsic defects related to the at least one element from Group VI withthe co-dopant.
 12. A method for forming a co-doped semiconductormaterial containing a first element from Group II of the periodic tableand a second element from Group VI of the periodic table, the methodcomprising: selecting a first dopant from elements in Group III or GroupVII of the periodic table based on a target resistivity of thesemiconductor material; determining a formation energy of a compoundcontaining a rare earth metal and at least one of the first element andthe second element; and selecting the rare earth metal as a seconddopant based on the determined formation energy and a target thresholdof formation energy.
 13. The method of claim 12 wherein determining theformation energy includes determining at least one of an enthalpy offormation and an entropy of formation of the compound containing therare earth metal and at least one of the first element and the secondelement.
 14. The method of claim 12 wherein if the formation energy isabove the target threshold, selecting the rare earth metal as the seconddopant.
 15. The method of claim 12 wherein the determined formationenergy corresponds to a heat of formation of the compound containing therare earth metal and at least one of the first element and the secondelement, and wherein if the heat of formation is above the targetthreshold, selecting the rare earth metal as the second dopant.
 16. Themethod of claim 12 wherein: the second element contains tellurium (Te);the rare earth metal contains erbium (Er); and determining the formationenergy includes determining a formation energy of Er—Te complexes. 17.The method of claim 12 wherein: the second element contains tellurium(Te); the rare earth metal contains erbium (Er); determining theformation energy includes determining a formation energy of Er—Tecomplexes; comparing the determined formation energy of Er-Te complexesto the target threshold; and if the determined formation energy of Er-Tecomplexes is greater than the target threshold, selecting erbium (Er) asthe second dopant.
 18. The method of claim 12 wherein determining theformation energy includes determining if the rare earth metal combineswith at least one of the first element and the second elementirreversibly to form the compound in a liquid phase.
 19. The method ofclaim 12 wherein determining the formation energy includes determiningif a reaction product between the rare earth metal and at least one ofthe first element and the second element form stable solid domains inthe bulk semiconductor material.
 20. The method of claim 12, furthercomprising selecting a concentration of the second dopant based on atarget depletion characteristic of the semiconductor material.
 21. Themethod of claim 20 wherein the target depletion characteristic includesa target charge carrier mobility and lifetime, and wherein selecting theconcentration of the second dopant includes selecting a concentration ofthe second dopant based on the target charge carrier mobility andlifetime.
 22. The method of claim 20 wherein the target depletioncharacteristic includes full depletion under a bias voltage, and whereinselecting the concentration of the second dopant includes selecting aconcentration of the second dopant to achieve the full depletion underthe bias voltage.
 23. The method of claim 20 wherein the selected seconddopant contains erbium (Er), and wherein selecting the concentration ofthe second dopant includes selecting a concentration of the seconddopant to be about 10 to about 400,000 atomic parts per billion.
 24. Amethod for forming a co-doped semiconductor material, comprising:forming a mixture with at least one element from Group II of theperiodic table, at least one element from Group VI of the periodic tablein a container, a first dopant, and a second dopant, wherein the firstdopant includes at least one element from Group III or VII of theperiodic table, and wherein the second dopant contains erbium (Er) ordysprosium (Dy); adjusting a concentration of the second dopant in themixture based on a target depletion characteristic of the semiconductormaterial; and converting the mixture into a solid material.
 25. Themethod of claim 24 wherein the target depletion characteristic includesa charge carrier mobility and lifetime, and wherein adjusting theconcentration of the second dopant includes adjusting a molarconcentration of the second dopant based on the target charge carriermobility and lifetime.
 26. The method of claim 24 wherein: the targetdepletion characteristic includes a charge carrier mobility andlifetime; the second dopant contains erbium (Er); and adjusting theconcentration of the second dopant includes increasing a molarconcentration of erbium (Er) in the mixture to increase the chargecarrier mobility and lifetime of the semiconductor material.
 27. Themethod of claim 24 wherein: the second dopant contains erbium (Er); andadjusting the concentration of the second dopant includes adjusting amolar concentration of erbium (Er) in the mixture between about 10 toabout 400,000 atomic parts per billion.
 28. The method of claim 24wherein: the second dopant contains erbium (Er); and adjusting theconcentration of the second dopant includes adjusting a molarconcentration of erbium (Er) in the mixture between about 10 to about10,000 atomic parts per billion.
 29. The method of claim 24 wherein: thesecond dopant contains erbium (Er); and adjusting the concentration ofthe second dopant includes adjusting a molar concentration of erbium(Er) in the mixture between about 10 to about 20,000 atomic parts perbillion.
 30. The method of claim 24 wherein: the second dopant containserbium (Er); and adjusting the concentration of the second dopantincludes adjusting a molar concentration of erbium (Er) in the mixturebetween about 10 to about 200,000 atomic parts per billion.